I hadn't heard this song before. The lyrics are very simple:

William (Willum) he had seven sons, seven sons, seven sons,
William he had seven sons, and this is what they did:
Number one was chopping wood, chopping wood, chopping wood,
Number one was chopping wood, and that is what he did.

Number two jumped up and down...
Number three was stacking wood...
Number four was hammering...
Number five was painting doors....
Number six was clapping...
Number seven was sleeping....

Here's a very nice performance:

https://www.youtube.com/watch?v=dzvXaGD-Qj0

Here's notation for the melody:

http://kristinbamberger.com/wp-content/uploads/2015/07/William-He-Had-Seven-Sons.pdf

It's not in any of the school music books that we have indexed. I gather from my Google search that the song is used in the Kodaly music program.